学校表格要求填写学生的性别。

The school form requires ___you to fill in the student's ___sex.

他们决定在结婚前不发生性关系。

They decided not to have ___sex before marriage.

兽医通过检查羽毛来确定这只鸟的性别。

The vet ___determines the sex of the bird by checking its feathers.